1. Field of the Invention
This invention relates to a tube tightener for downhole use in production and exploration wells.
2. Description of the Prior Art
After a string of tubing is run down a wellbore, it requires to be tightened so that the tubing is securely and centrally located in the bore. It can also happen that the tubing becomes loose after it has been in the well for a length of time, due to the action of downhole pumps or other equipment to which the tightener is attached, which also requires that the tubing string be tightened. A wide variety of tubing anchors have been proposed for this purpose, such anchors using slips which are forced outwardly into gripping engagement with the wellbore once the tubing string is in position. Some devices use a threaded rotation of the tubing string to set the slips but this can be difficult or impossible to release for withdrawal or re-location of the tubing string. Drilling or fishing operations then become necessary to remove the anchor. Other methods use a cone arrangement with a shear system to set the slips, but this often results in shearing of the tool due to the force exerted on the cone. Also, the anchors tends to become contaminated with sand during normal operation in the wellbore and release of the anchor for removal or relocation of the tubing string then becomes difficult or impossible.
One attempt to overcome the foregoing problems is described in Canadian Patent No. 1,274,470 (Weber). Weber's approach is to use slips extending radially outwardly through apertures in a slip casing and biased radially inwardly (i.e. away from the wellbore surface) by means of springs. An inner mandrel is connected for rotation with a tubing string and has on its outer surface a series of cams which can be rotated into engagement with the rear surface of the slips by rotation of the inner mandrel, which forces the slips outwardly against the force of the springs into engagement with the wellbore surface. The rotation of the inner mandrel to set the anchor is effected by rotating the tubing string. The slips have vertically extending teeth which bite into the wellbore surface and lock the anchor in position. In order to restrain the slips from rotating with the inner mandrel during the setting operation, which would prevent the necessary relative movement between the cams and the slips, a drag block casing is secured to the slip casing and is provided with a number of drag blocks, which are biased outwardly by springs into engagement with the wellbore surface. These drag blocks restrain rotational movement but permit vertical movement of the anchor and tubing string.
However, there are a number of drawbacks to the Weber device, which the present invention seeks to overcome. The Weber device is primarily designed for operation with a screw-type pump in which the pump operates by rotating the rod string to the right when viewed from its upper end. Thus, the device is also designed to be set by rotating the inner mandrel to the right (i.e., clockwise) and released by rotating anti-clockwise. However, there are many other situations where the tubing tightener should be manipulated in the opposite direction but the Weber tool does not provide flexibility in that regard. Furthermore, the Weber device is unnecessarily complex and unwieldy in that it employs separate slips and drag blocks. This decreases the bypass around the tool.
It would therefore be desirable to provide a tubing tightener which can easily be adapted to either clockwise or anti-clockwise setting, depending upon user requirements. It would also be desirable that the slips and drag blocks be integrated in order to increase the bypass around the tool and reduce the weight and length of the device, it being noted that increased weight and length can make removal or relocation of the device more difficult.